Microporous sheet product and methods for making and using the same

Abstract

Microporous sheet product and methods of making and using the same. In one embodiment, the microporous sheet product is made by a process that includes melt-extruding a sheet material using an extrusion mixture that includes a thermoplastic polymer, a superabsorbent polymer, and a compatibilizing agent. After extrusion, the compatibilizing agent may be removed from the sheet material. When the sheet product is imbibed with a polar or ion-containing liquid, the superabsorbent polymer swells, causing a reduction in the pore size of the sheet product. The exposure also causes some of the superabsorbent polymer to migrate to the exterior of the microporous sheet product. The microporous sheet product may be used, for example, as a battery separator, as a food packaging material, as a diffusion barrier in the ultrafiltration of colloidal matter, and in disposable garments.

What is claimed is: 
     
       1. A microporous sheet product, the microporous sheet product made by a method comprising melt-extruding an extrusion mixture to produce a sheet material in film form and then cooling the sheet material, the extrusion mixture comprising a thermoplastic polymer, a superabsorbent polymer, and a compatibilizing agent, the compatibilizing agent promoting mixing of the thermoplastic polymer and the superabsorbent polymer and forming, by phase-separation, micropores in the sheet material, wherein the microporous sheet product is a single layer, wherein the microporous sheet product has capillary porosity suitable for liquid electrolyte conductivity, wherein the microporous sheet product, even without being stretched and/or even without having the compatibilizing agent removed, comprises an open-celled matrix of the thermoplastic polymer in which the superabsorbent polymer is dispersed, wherein the microporous sheet product is un-stretched, wherein the compatibilizing agent is retained in situ, and wherein a portion of the superabsorbent polymer migrates from within the open-celled matrix to an exterior surface of the open-celled matrix after exposure of the microporous sheet product to a polar or ion-containing liquid for absorption. 
     
     
       2. The microporous sheet product as claimed in  claim 1  wherein the thermoplastic polymer comprises one or more thermoplastic polymers selected from the group consisting of polyolefins, polyamides, polyethylene terephthalate, polyacrylics, and polyvinyl acetate. 
     
     
       3. The microporous sheet product as claimed in  claim 2  wherein the thermoplastic polymer comprises a polyolefin. 
     
     
       4. The microporous sheet product as claimed in  claim 3  wherein the thermoplastic polymer comprises a polyethylene. 
     
     
       5. The microporous sheet product as claimed in  claim 2  wherein the thermoplastic polymer comprises a polyamide. 
     
     
       6. The microporous sheet product as claimed in  claim 1  wherein the thermoplastic polymer constitutes about 15-80% by volume of the extrusion mixture. 
     
     
       7. The microporous sheet product as claimed in  claim 1  wherein the superabsorbent polymer comprises one or more superabsorbent polymers selected from the group consisting of cross-linked polyacrylates, methacrylates, polyacrylamides, carboxymethyl celluloses, polyvinyl alcohol copolymers, polyethylene oxides, starch-grafted copolyacrylates or polyacrylamides, and ethylene maleic anhydride copolymers. 
     
     
       8. The microporous sheet product as claimed in  claim 7  wherein the superabsorbent polymer comprises a cross-linked polyacrylate. 
     
     
       9. The microporous sheet product as claimed in  claim 1  wherein the superabsorbent polymer is in particle form and has a particle size smaller than about 30 microns. 
     
     
       10. The microporous sheet product as claimed in  claim 9  wherein the superabsorbent polymer has a particle size of between 1 to 10 microns. 
     
     
       11. The microporous sheet product as claimed in  claim 1  wherein the superabsorbent polymer constitutes about 1-80% by volume of the extrusion mixture. 
     
     
       12. The microporous sheet product as claimed in  claim 11  wherein the superabsorbent polymer constitutes about 22-40% by volume of the extrusion mixture. 
     
     
       13. The microporous sheet product as claimed in  claim 1  wherein the compatibilizing agent is selected from the group consisting of plasticizers and surfactants. 
     
     
       14. The microporous sheet product as claimed in  claim 13  wherein the plasticizer is selected from the group consisting of polyethylene oxide, polyethylene glycol, hydroxypropylene, phthalates, mineral oil, and mineral spirits. 
     
     
       15. The microporous sheet product as claimed in  claim 1  wherein the compatibilizing agent is mineral spirits. 
     
     
       16. The microporous sheet product as claimed in  claim 1  wherein the compatibilizing agent constitutes about 1-80% by volume of the extrusion mixture. 
     
     
       17. The microporous sheet product as claimed in  claim 16  wherein the compatibilizing agent constitutes about 10-50% by volume of the extrusion mixture. 
     
     
       18. The microporous sheet product as claimed in  claim 1  wherein the thermoplastic polymer constitutes about 15-80% by volume of the extrusion mixture, wherein the superabsorbent polymer constitutes about 1-80% by volume of the extrusion mixture, and wherein the compatibilizing agent constitutes about 1-80% by volume of the extrusion mixture. 
     
     
       19. The microporous sheet product as claimed in  claim 1  wherein the extrusion mixture further comprises an inorganic oxide. 
     
     
       20. The microporous sheet product as claimed in  claim 19  wherein the inorganic oxide constitutes up to about 20% by volume of the extrusion mixture. 
     
     
       21. The microporous sheet product as claimed in  claim 1  wherein the superabsorbent polymer has a solubility parameter above 11 and wherein at least one of the thermoplastic material and the compatibilizing agent has a solubility parameter above 11. 
     
     
       22. The microporous sheet product as claimed in  claim 21  wherein the thermoplastic polymer has a solubility parameter above 11. 
     
     
       23. The microporous sheet product as claimed in  claim 21  wherein the compatibilizing agent has a solubility parameter above 11. 
     
     
       24. The microporous sheet product as claimed in  claim 1  wherein the microporous sheet product has a resistivity below 1,000 ohm-cm as tested in a 30% KOH solution. 
     
     
       25. The microporous sheet product as claimed in  claim 24  wherein the microporous sheet product has a resistivity below about 500 ohm-cm as tested in a 30% KOH solution. 
     
     
       26. The microporous sheet product as claimed in  claim 25  wherein the microporous sheet product has a resistivity below 100 ohm-cm as tested in a 30% KOH solution. 
     
     
       27. The microporous sheet product as claimed in  claim 1  wherein the microporous sheet product experiences a weight loss of at least 20% of the superabsorbent polymer when soaked in 30% KOH solution for 2 days. 
     
     
       28. The microporous sheet product as claimed in  claim 1  wherein the microporous sheet product has an average pore size below 5 microns. 
     
     
       29. The microporous sheet product as claimed in  claim 1  wherein the microporous sheet product increases in thickness by at least 5% after exposure to a liquid for absorption. 
     
     
       30. The microporous sheet product as claimed in  claim 1  wherein the melt-extruding comprises feeding the extrusion mixture into a first barrel of an extruder and injecting a liquid plasticizer into a subsequent barrel of the extruder and evacuating any potential volatiles using an open barrel of the extruder. 
     
     
       31. The microporous sheet product as claimed in  claim 1  wherein the compatibilizing agent is mineral oil. 
     
     
       32. The microporous sheet product as claimed in  claim 1  wherein the superabsorbent polymer is in particle form and has a particle size, wherein the microporous sheet product has a pore size, and wherein the particle size of the superabsorbent polymer is greater than the pore size of the microporous sheet product. 
     
     
       33. The microporous sheet product as claimed in  claim 1  wherein the cooling comprises immersing the sheet material in a cooling bath. 
     
     
       34. The microporous sheet product as claimed in  claim 1  wherein the superabsorbent polymer comprises a functional cation. 
     
     
       35. A microporous sheet product, the microporous sheet product made by a method comprising melt-extruding an extrusion mixture to produce a sheet material in film form and then cooling the sheet material, the extrusion mixture consisting of a thermoplastic polymer, a superabsorbent polymer, and a compatibilizing agent, wherein the superabsorbent polymer is a cross-linked lithium polyacrylate, the compatibilizing agent promoting mixing of the thermoplastic polymer and the superabsorbent polymer and forming, by phase-separation, micropores in the sheet material, wherein the microporous sheet product is a single layer, wherein the microporous sheet product has capillary porosity suitable for liquid electrolyte conductivity, wherein the microporous sheet product, even without being stretched and/or even without having the compatibilizing agent removed, comprises an open-celled matrix of the thermoplastic polymer in which the superabsorbent polymer is dispersed, and wherein a portion of the superabsorbent polymer migrates from within the open-celled matrix to an exterior surface of the open-celled matrix after exposure of the microporous sheet product to a polar or ion-containing liquid for absorption. 
     
     
       36. The microporous sheet product as claimed in  claim 35  wherein the method further comprises removing the compatibilizing agent from the sheet material. 
     
     
       37. The microporous sheet product as claimed in  claim 36  wherein the step of removing the compatibilizing agent comprises vaporizing the compatibilizing agent. 
     
     
       38. The microporous sheet product as claimed in  claim 36  wherein the microporous sheet product has at least 10% of its volume in capillary porosity as micropores. 
     
     
       39. A method of separating the electrodes of a battery, the method comprising positioning the microporous sheet product of  claim 36  between the electrodes. 
     
     
       40. A method of preparing a food packaging material, the method comprising the steps of:
 (a) providing the microporous sheet product of  claim 1 ; and 
 (b) then, imbibing the microporous sheet product with a liquid smoke extract flavoring. 
 
     
     
       41. A food packaging material made by the method of  claim 40 . 
     
     
       42. A multilayer sheet product, the multilayer sheet product comprising a plurality of stacked layers, wherein at least one of the stacked layers is the microporous sheet product of  claim 1 . 
     
     
       43. A multilayer sheet product, the multilayer sheet product comprising a first layer and a second layer, the first layer and the second layer being in direct contact with one another, the first layer comprising the microporous sheet product of  claim 1 , the second layer being devoid of a superabsorbent polymer. 
     
     
       44. A method of packaging a food item, the method comprising contacting the food item with the microporous sheet product of  claim 1 . 
     
     
       45. A multilayer sheet product, the multilayer sheet product comprising a first layer and a second layer, the first layer and the second layer being in direct contact with one another, the first layer comprising the microporous sheet product of  claim 1 , the second layer being a nonwoven structure. 
     
     
       46. The multilayer sheet product as claimed in  claim 43  wherein a portion of the superabsorbent polymer migrates from the first layer to the second layer after exposure of the multilayer sheet product to a polar or ion-containing liquid for absorption.